Tractor trailer or “semi” trailer trucks are well known and widely used to haul a wide range of goods across great distances. A conventional tractor trailer truck includes a tractor that pulls a trailer. A conventional tractor includes an engine, a cabin for the driver, and, in some instances, a sleeper compartment. A conventional trailer is used to haul a variety of goods and may take various forms, ranging from a box-like container with an enclosed cargo space to a flatbed to a car hauler. The prior art also includes box trucks that provide a truck with an attached bed. As described herein, the various implementations of the invention are applicable to all trucks and vehicles that utilize air brakes and hydraulic fluid brakes.
Due to their substantial size and weight, tractor trailer trucks conventionally use air pressure, rather than standard hydraulic fluid, to actuate the brakes. Not only does an air pressure brake system provide greater braking power, it reduces the potential for certain problems with conventional hydraulic brake systems such as leakage or vaporization of the hydraulic brake fluid. Further, because the tractor brake system may be connected with the trailer brake system, it is more convenient to use an air pressure system because it allows for a tractor to be connected to multiple trailers.
The parking brake of the tractor and the emergency brake of the trailer are conventionally spring brakes that also operate on air pressure. The springs cause the brakes to be applied. More particularly, the tractor's parking brake and the trailer's emergency brake require air pressure in order to be released. When air pressure is applied to the tractor trailer truck braking system, the parking brake and the emergency brake are released. In contrast, when air pressure is released from the tractor trailer truck braking system, the parking brake and the emergency brake are applied by action of the springs. In this way, the truck driver may be assured that if air pressure is inadvertently released or lost from the braking system, the trailer will brake to a stop instead of not being braked and, perhaps, becoming uncontrollable.
Further, a truck driver conventionally applies tractor and trailer parking brakes by operating valves that either deliver or release compressed air to the brake system. More particularly, a tractor conventionally includes a tractor parking brake valve and a trailer parking brake valve. Once the driver has positioned the tractor and trailer as desired, the driver will manipulate the tractor parking brake valve to release compressed air from the tractor brake system and thereby apply the tractor parking brakes. Similarly, the driver will manipulate the trailer parking brake valve to release compressed air from the trailer brake system and thereby apply the trailer parking brakes. It is also known to provide for the two valves to cooperate such that when the truck driver manipulates the tractor parking brake valve, the trailer parking brake valve is simultaneously activated so that both the tractor and trailer parking brakes are applied.
With specific reference to the parking or emergency brake for the trailer, the valve is manipulated by the truck driver to supply compressed air to the trailer emergency brake system and release the brakes. In this manner, the truck driver can release the trailer emergency brake in order to pull the trailer away from the dock. By virtue of the foregoing arrangement, the truck driver is also able to release the tractor parking brake and pull the tractor away from the trailer without releasing the trailer parking brakes. Once the truck driver re-connects the tractor to the trailer and seeks to again move the trailer, the driver can manipulate the trailer emergency brake valve (in the tractor) to deliver compressed air to the trailer brake system and release the parking brakes.
In use, a trailer is conventionally loaded and unloaded at a loading dock. The tractor trailer truck operator maneuvers the trailer into position by backing the tractor and trailer up against the loading dock in such a way that the dock surface is substantially level with the surface of the trailer. The rearward most portion of the trailer is positioned adjacent to the loading dock so that a forklift or like equipment may be driven onto the trailers floor surface to unload or load the trailer.
A safety problem exists in the loading or unloading of trailers. For example, if a trailer is moved away from the dock before the forklift operator or other dock worker completes loading or unloading of the trailer, the dock worker or equipment may be jeopardized. The worker or product or forklift may fall between the rear edge of the trailer and the loading dock, causing harm to the worker or damage to the goods or the equipment. The truck driver may inadvertently pull the trailer away from the dock without knowing or realizing that the loading or unloading process is not complete. For these and other reasons, it is preferable that a trailer not be prematurely or inadvertently pulled away from the dock, or that the truck driver be alerted to the fact that the trailer is in use. There is a need in the art for a device and method that addresses premature or inadvertent movement of a trailer from a dock.